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Full text of "Text Book Of Mechanical Engineering"


i;

444                  Combined Bending Moments.

by superposing the results due to the separate loads, having regard
to the signs + and -.    The cases are as follows:

(i.) One distributed and two concentrated loads on cantilever.
(2.) One concentrated and one distributed load on girder.
(3.) Maximum diagram for rolling load.
(4.) Three concentrated loads and one distributed load on girder.

The distributed load is more conveniently placed on one side
of the base line, and the concentrated loads on the other side,
in the superposed diagram. All are well lettered to shew the
relation between diagram and load. In Case (3) the load must
be placed over the successive numbers, and diagrams obtained for
every position, as in Fig. 397, then the bounding curve will be
the maximum, and the final maximum Em curve will be a parabola.

Fig. 403 shews a continuous beam on three supports, loaded
by equal concentrated loads, Wx and W1? and uniformly by its
own weight, W + W. The contra-flexure points are practically
the same for each case, and the diagrams can be obtained from
previous considerations (see p. 953). The following table is very
useful for continuous beams: